13 The Forest Margins of Sumatra, Indonesia

Indonesia still has large forest areas, but they are rapidly being converted to other land uses. Transformation from primary to secondary forest is caused largely by timber extraction, and traditional shifting cultivation systems play a smaller role. Subsequent transformation of secondary and logged-over for-est types generally is based on slash-and-burn practices by large-scale farmers and smallholders for a variety of reasons. Migrants convert part of the forest to temporary cropland either in government-sponsored schemes or spontane-ously. Such land can evolve into alang-alang (Imperata cylindrica [L.]) grass-lands or into permanent tree-based production systems (agroforests). Slash-and-burn is both a land-clearing technique and a land use system. It is inaccurate to equate slash-and-burn agriculture only with permanent for-est conversion and unsustainable land use. The technique is attractive because fire is the cheapest, most effective way to clear land (Ketterings et al. 1999). The Alternatives to Slash and Burn (asb) characterization data (van Noord-wijk et al. 1995, 1998; Tomich et al. 1998) suggest that in Jambi (Sumatra), most slash-and-burn is used for replacing old jungle rubber, rather than fo